Core-shell polymer particles

Abstract

A core-shell particle for use as filler in rubber compositions. In one embodiment, the particle comprises a crosslinked core having repeat aromatic vinyl units. During an emulsion polymerization, a crosslinked shell comprising of conjugated diene units is grafted onto the core through residual vinyl units. The polymeric shell provides for better interaction and dispersion of the styrene core in an otherwise immiscible polymer matrix, particularly diene-based polymers. In another embodiment, the core has repeat units of (i) about 0% to about 25% by weight of a conjugated diene unit, (ii) about 70% to about 85% by weight of an aromatic vinyl unit, and (iii) about 15% to about 30% by weight of a crosslinking monomer unit.

What we claim is:  
     
       1. A polymeric particle comprising: 
       (a) a polymeric core, the core comprising repeat units comprised of styrene; and,  
       (b) a polymeric shell, the shell comprising repeat units comprised of 1,3-butadiene wherein the polymeric particle has a particle diameter of less than about 240 nm.  
     
     
       2. The polymeric particle of  claim 1  wherein the polymeric core is copolymerized styrene and butadiene. 
     
     
       3. The polymeric particle of  claim 2  wherein the styrene is about 70 to 100% and the butadiene is about 0 to 30%. 
     
     
       4. The polymeric particle of  claim 3  wherein the core includes an outer surface and, wherein the shell is grafted to the outer surface. 
     
     
       5. The polymeric particle of  claim 4  wherein the shell is 1,3-butadiene and styrene. 
     
     
       6. The polymeric particle of  claim 5  wherein the core is about 70 to 85% styrene and about 15 to 30% butadiene and the shell is about 20 to 30% styrene and about 70 to 80% butadiene. 
     
     
       7. The polymeric particle of  claim 6  wherein the core is about 70 to 85% styrene and about 15 to 30% butadiene and the shell is 23.5% styrene and 76.5% butadiene. 
     
     
       8. A method of forming a polymeric particle comprising the steps of: 
       (a) emulsion polymerizing styrene and about 0% to 100% by weight of 1,3-butadiene, and crosslinking divinyl benzene to create a crosslinked polymeric core having residual vinyl groups;  
       (b) emulsion polymerizing 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell; and,  
       (c) grafting the polymeric shell to the polymeric core through covalently bonding of the polymeric shell with the residual vinyl groups of the polymeric core.  
     
     
       9. A method of forming a polymeric particle comprising the step of: 
       emulsion polymerizing styrene to create a crosslinked polymeric core having residual vinyl groups;  
       emulsion polymerizing 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell; and,  
       grafting the polymeric shell to the polymeric core through covalently bonding of the polymeric shell with the residual vinyl groups of the polymeric core.  
     
     
       10. The method of  claim 9 , wherein emulsion polymerizing styrene to create a crosslinked polymeric core having residual vinyl groups further comprises the step of: 
       emulsion polymerizing styrene and butadiene to create a crosslinked polymeric core having residual vinyl groups.  
     
     
       11. The method of  claim 10 , wherein emulsion polymerizing styrene and butadiene to create a crosslinked polymeric core having residual vinyl groups further comprises the step of: 
       emulsion copolymerizing styrene and butadiene to create a crosslinked polymeric core having residual vinyl groups.  
     
     
       12. The method of  claim 11 , wherein emulsion copolymerizing styrene and butadiene to create a crosslinked polymeric core having residual vinyl groups further comprises the step of: 
       emulsion copolymerizing about 70 to 100% styrene and about 0 to 30% butadiene to create a crosslinked polymeric core having residual vinyl groups.  
     
     
       13. The method of  claim 12 , wherein emulsion copolymerizing about 70 to 100% styrene and about 0 to 30% butadiene to create a crosslinked polymeric core having residual vinyl groups further comprises the step of: 
       emulsion copolymerizing about 70 to 85% styrene and about 15 to 30% butadiene to create a crosslinked polymeric core having residual vinyl groups.  
     
     
       14. The method of  claim 9 , wherein emulsion polymerizing 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell further comprises the step of: 
       emulsion copolymerizing styrene and 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell.  
     
     
       15. The method of  claim 14 , wherein emulsion copolymerizing styrene and 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell further comprises the step of: 
       emulsion copolymerizing 23.5% styrene and 76.5% 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell.  
     
     
       16. The method of  claim 13 , wherein emulsion polymerizing 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell further comprises the step of: 
       emulsion copolymerizing styrene and 1,3-butadiene in the presence of the core to create a crosslinlked polymeric shell.  
     
     
       17. The method of  claim 16 , wherein emulsion copolymerizing styrene and 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell further comprises the step of: 
       emulsion copolymerizing 23.5% styrene and 76.5% 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell.  
     
     
       18. The method of  claim 9 , wherein the method further comprises the step of: 
       crosslinking divinyl benzene with the styrene to create a crosslinked polymeric core.  
     
     
       19. The method of  claim 13 , wherein the method further comprises the step of: 
       crosslinking divinyl benzene with the styrene to create a crosslinked polymeric core.  
     
     
       20. The method of  claim 14 , wherein the method further comprises the step of: 
       crosslinking divinyl benzene with the styrene to create a crosslinked polymeric core.  
     
     
       21. The method of  claim 16 , wherein the method further comprises the step of: 
       crosslinking divinyl benzene with the styrene to create a crosslinked polymeric core.  
     
     
       22. A method of forming a polymeric particle comprising the step of: 
       emulsion polymerizing butadiene to create a crosslinked polymeric core having residual vinyl groups;  
       emulsion polymerizing 1,3-butadiene in the presence of the core to create a crosslinked polymeric shell; and,  
       grafting the polymeric shell to the polymeric core through covalently bonding of the polymeric shell with the residual vinyl groups of the polymeric core.  
     
     
       23. The method of  claim 22 , wherein the method further comprises the step of: 
       crosslinking divinyl benzene with the butadiene to create a crosslinked polymeric core.